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Old 24th October 2003, 01:55 AM   #1
PassFan is offline PassFan  United States
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Unhappy Power supply problem

Well, I turned on my amp today and my rectifier tube started flashing blue and white and burning and then stopped due to the primary fuse blowing. The fuse must have blown due to the current draw. They were 2.5 amps. This amp has been working fine for over a month.
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Old 24th October 2003, 02:05 AM   #2
Colt45 is offline Colt45  Serbia
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theres a short somewhere on the secondary side.. could be the filter caps, but it could be something else too. i suppose it could be the rectifier itself as well.
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Old 24th October 2003, 02:08 AM   #3
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Hi,

Quote:
suppose it could be the rectifier itself as well.
That's what I suspect.

Cheers,
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Frank
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Old 24th October 2003, 08:25 PM   #4
PassFan is offline PassFan  United States
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I plugged another rectifier tube in and promptly burned it up. So I will have to go a looking. Thanks
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Old 24th October 2003, 09:09 PM   #5
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Quote:
Originally posted by PassFan
I plugged another rectifier tube in and promptly burned it up. So I will have to go a looking. Thanks
Try using a pair if 1n4007 (assuming FW) and a beefy series resistor in place of the tube whilst testing. Cheaper than blowing tubes.
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Old 24th October 2003, 09:27 PM   #6
Colt45 is offline Colt45  Serbia
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check all over for shorts.. lets see. try..

filter caps

choke - if its shorted there could be way too much C on the rectifier.

the tubes could have an internal short, but if this was the case, generally a cathode resistor would go before the rectifier does, its possible you have no Rk though. (fixed bias, although even when fixed bias is used, a 10om resistor is generally put in the position of Rk, not for biasing but to check current levels easily)

just look anywhere for a short from B+ to ground.
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Old 24th October 2003, 10:03 PM   #7
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Default Check up

I would first make sure all voltages are zero volts. Make sure the line cord is unplugged.

Unplug the rectifier (in case the tube is directly shorted).

Using a meter type ohmmeter (not digital), measure the resistance from B+, at the rectifier filament pins, to ground. Use, say, the X10k scale. The meter should go to zero and gradually return to infinity. Leave it on for 30-60 seconds. If the meter stays on zero, there is a direct short to ground. If it goes up to say, 1 meg, the capacitors are probably ok.

If the meter stays on zero, I would disconnect the power suply part about 1/2 the way down the "line" and see if the reading "jumps" off of zero. If it reads near infinity ohms, the problem is past the disconnected part. If the reading stays at zero, the problem is in the power supply section before the disconnect.

Once you find which half of the power supply is causing the problem, you can individually disconnect parts until you find the culprit.

If you want to check a choke or rectifier filament winding, disconnect both leads and measure. Use the X1 meg scale if it has one. If not, then the X100k scale. The reading should be infinity. Even if the reading is, say 1 or 10 meg to gound, I would suspect the choke or filament winding.

Also check the tube sockets, if all else fails.

Hope this helps.
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